Free cutting alloys



Patented Jan. 7,, 1936 UNITED STATES man CUTTING more;

Walter A. Dean and Charles G. Jan'cura, Cleveland, Ohio, assignors to Aluminum Company of America, Pittsburgh, l a., a corporation of Pennsylvania 130 Drawing.

Application September is, 1933,

' Serial No. 689,888

3 Claims.

The invention relates to aluminum-copper alloys and is particularly concerned with alloys of this nature containing substantial amounts of.

cal cutting operations, however, such as boring,

drilling, planing or lathe-cutting are successfully carried out only by using certain precautions which increase the expense oi the operation and which occasionally necessitate the use of another alloy which may be machined more readily but which is otherwise not so desirable from the standpoint of physical properties. When alloys are diflicult to machine this disadvantage'becomes evident in many cases through rapid wear of the cutting tool edge which necessitates frequent resharpening. In such cases, where machining is difiicult, continual lubrication is required. The machined surface is rough and irregular and the chip has a tendency to form continuous curls or spirals that may foul the tool or the operating parts of the machine. These drawbacks retard production and increase the cost of operation. Many articles require a variety of machining operations before being applied to their final purpose'and it is particularly desirable that these aiiiticles be finished economically and satisfactoi Y.

An object of this invention, therefore, is the production of alloys containing substantial amounts of copper which may be readily machined.

A further object is the production of such an alloy whose mechanical properties in the preferred composition range are not essentially altered in any material manner except for the aforesaid improvement in machining.

These objects we haveeffected by the addition of one or both ofthe elements lead and thallium in amount between about 0.05 per cent and 10.0

5 per cent'of each. In our preferred practice, however, less than 5 per cent of either element is generally employed to impart the desired degree of machinability. For the purpose of our invention these elements are substantially equivalent,their behavior in the alloys of the class herein described being similar in respect to machining characteristics. N

We have discovered that the simultaneous presence of lead and thallium in aluminum base alloys containing copper is more advantageous than that of the same total amountoi either of the elements used separately. For instance, the addition 01 0.5 per cent of lead and 0.5 'per cent of thallium produces a more distinct improvement in machining characteristics than the addition of 1.0 per cent of lead or 1.0 per cent of thallium separately. 1

When lead and thallium within the disclosed range are added to aluminum-copper alloys containing from 2 percent to 12 per cent of copper, 15

- the resulting alloys may be subjected to mechanical cutting operations with considerably greater economy by reason, for instance, oi greater allowable cutting-speed. In addition, articles which were formerly commercially impractical to pro- 20 duce can now be readily fabricated, the chips being brittle and easy to handle and the machined surfacebeing smooth and -satisfactory. Generally speaking, the lower the copper content, the greater the amount of lead and/or thallium re- 25 quired to produce a standard effect. I Ifthe aluminum-copper alloy is made up to contain only one of the elements lead or thallium we prefer to use about 1.5 per cent of lead or 1.5 per cent of thallium in an alloy containing about 6.0 per cent of copper. Analuminum base alloy containing the same amount of copper but both of the elements lead and thallium in combination will require only about 0.5 per cent of each to produce approximatelythe samemachin- 35 ing qualities. The physical properties of an aluminum-copper .alloy-as hereinabove disclosed are not substantially. affected by the addition of the aforesaid free machining constituents in an amount up to 40 about 5.0 per cent total. For this reason we preier to use less'than 5 per cent of either element alone or in combination. If the total amount l exceeds this figure there becomes apparent a tall ing ofi in physical properties which is compensated for'by an increase in the ease of machining, and there are applications wherein a compromise of this nature may be desirable.

The lead or thallium is most conveniently added to the alloy by introducing these constituents in solid form into a molten heat of the aluminum I base alloy since they melt at a temperature coni'oundry. II amounts in excess of about 1.5 per cent of the total of lead and thallium are retemperature and vigorously stirred to assure a thorough mixture of the alloying constituents.

The method here referred to is more fully described in co-pending application, Serial No. 689,885 filed September 18, 1933.

The alloys herein disclosed may be subjected to the usual thermal treatments familiar to those skilled in the art for the purpose of improving or altering their physical characteristics.

The term aluminum used herein and in the appended claims embraces the usual impurities found in aluminum ingot of commercial grade, or

picked up in the course of the usual handling operations incident to ordinary melting practice.

We claim:

1. An aluminum-copper alloy containing from about 2 per centto about 12 per cent of copper 5 and from about 0.05 per cent to 10 per cent of lead, the balance being aluminum.

2. An aluminum-copper alloy containing from about 2 per cent to about 12 per cent of copper I and from about 0.05 per cent to 5 per cent of 10 lead, the balance being aluminum.

3. An aluminum-copper alloy containing about 6.0 per cent of copper and about 1.5 per cent of lead, the balance being aluminum.

WALTER A. DEAN. 15 CHARLES G. JANCURA. 

